The present invention is related to machines used in performing railway right-of-way maintenance, and specifically to a machine for driving railroad rail fasteners such as lag screws or nuts into or onto railroad track ties using an axially rotatable motion.
Conventional railroad rails are secured to the ties by so-called cut spikes which are driven by vertically directed forces through tie plate apertures into the wooden railroad ties. However, it has been found that certain portions of track, such as those bearing high tonnage traffic, as well as curved track sections, wear out faster than others, and require more frequent replacement. A side effect of frequent rail replacement is that the spikes have a tendency to loosen in the ties, especially in high tonnage sections of track.
As a result of these conditions, maintenance directors of railroads have determined that alternate fastening technologies to cut spikes should be explored. One alternative is to use so-called hairpin spikes, which have depending prongs designed to spread apart within the tie. Although hairpin spikes are used in some high traffic portions of track, they are somewhat limited in their application, in that such spikes are more difficult to drive into and pull from the ties using automatic equipment.
Another type of fastener which is being considered is the rail lag screw, which is similar in dimension to a cut spike, with the major difference being that the lag screw is designed to be axially rotated in the tie. As such the lag screw has a threaded shank and a polygonal head for engagement by driving tools.
Yet another type of alternate rail fastening system employs relatively permanent concrete ties having threaded studs embedded therein for securing the rails. Upon placement of a rail on the concrete ties, nuts are threaded onto the studs to secure the rail. One other type of fastener is a releasable clip, which is also preferably used with concrete ties.
A conventional technique for driving rail lag screws employs a hand-held rotary impact wrench which engages the head of the spike and can either drive or remove the lag screw at the direction of the operator. However, a major drawback of this technique is that during placement, either two operators are required, e.g. one to place the screws and one to operate the impact wrench, or a single operator must perform both tasks at an appreciably slower pace. Either way, this technique is inefficient and labor intensive.
Designers of conventional automatic spike driving machines have traditionally focused on the problems of rapidly, accurately and quietly driving cut spikes into the ties with vertically directed pushing and/or percussive forces without bending individual spikes. One example of a cut spike driving machine employing such vertical forces is commonly-assigned U.S. Pat. No. 5,191,840, which is incorporated by reference herein. However, in view of the relatively recent attention directed to alternate rail fastening technologies, designers of such equipment have not yet addressed the unique problems inherent with automatically handling, driving and removing lag screws or nuts.
Thus, there is a need for a machine which can automatically handle lag screws, and which permits an operator to drive them accurately, preferably into pre-drilled holes in the ties. There is also a need for a machine which will automatically remove the lag screws or other fasteners from the ties to permit the rapid replacement of rails on curves and high tonnage traffic areas.
Consequently, a first object of the present invention is to provide a device which can automatically drive alternate rail fasteners, such as lag screws and/or nuts.
Another object of the present invention is to provide a rail fastener driving device which can drive lag screws and/or nuts with minimum operator effort.
Still another object of the present invention is to provide a rail fastener driving device which features the capability of accurately aligning the fastener relative to the tie.
Yet another object of the present invention is to provide a rail lag screw driving device which positively engages the heads of the lag screws without causing deformation and/or misalignment of the screws.
A further object of the present invention is to provide a rail maintenance machine which is convertible from fastener applicating using an automatic device, to tie boring, using a device separately mounted to the machine.